Packages with Si-substrate-free interposer and method forming same

ABSTRACT

A method includes forming a plurality of dielectric layers, forming a plurality of redistribution lines in the plurality of dielectric layers, etching the plurality of dielectric layers to form an opening, filling the opening to form a through-dielectric via penetrating through the plurality of dielectric layers, forming a dielectric layer over the through-dielectric via and the plurality of dielectric layers, forming a plurality of bond pads in the dielectric layer, bonding a device die to the dielectric layer and a first portion of the plurality of bond pads through hybrid bonding, and bonding a die stack to through-silicon vias in the device die.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No. 16/680,809, filed Nov. 12, 2019, and entitled “Packages with Si-Substrate-Free Interposer and Method Forming Same,” which is a continuation of U.S. patent application Ser. No. 15/640,987, filed Jul. 3, 2017, and entitled “Packages with Si-Substrate-Free Interposer and Method Forming Same,” now U.S. Pat. No. 10,522,449, issued Dec. 31, 2019, which claims the benefit of the U.S. Provisional Application No. 62/483,813, filed Apr. 10, 2017, and entitled “Packages with Si-substrate-free Interposer and Method forming Same,” which applications are hereby incorporated herein by reference.

BACKGROUND

The packages of integrated circuits are becoming increasing complex, with more device dies packaged in the same package to achieve more functions. For example, a package may include a plurality of device dies such as processors and memory cubes bonded to a same interposer. The interposer may be formed based on a semiconductor substrate, with through-silicon vias formed in the semiconductor substrate to interconnect the features formed on the opposite sides of the interposer. A molding compound encapsulates the device dies therein. The package including the interposer and the device dies are further bonded to a package substrate. In addition, surface mount devices may also be bonded to the substrate. A heat spreader may be attached to the top surfaces of the device dies in order to dissipate the heat generated in the device dies. The heat spreader may have a skirt portion fixed onto the package substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1 through 28A illustrate the cross-sectional views of intermediate stages in the formation of silicon-substrate-free (Si-less) packages in accordance with some embodiments.

FIGS. 28B and 28C illustrate the cross-sectional views of packages including the Si-less packages in accordance with some embodiments.

FIGS. 29 and 30 illustrate the cross-sectional views of intermediate stages in the formation of Si-less packages in accordance with some embodiments.

FIGS. 31 and 32 illustrate the cross-sectional views of packages embedding Si-less packages in accordance with some embodiments

FIG. 33 illustrates a process flow for forming a package in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “underlying,” “below,” “lower,” “overlying,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

A package formed based on a silicon-substrate-free (Si-less) interposer and the method of forming the same are provided in accordance with various exemplary embodiments. The intermediate stages of forming the package are illustrated in accordance with some embodiments. Some variations of some embodiments are discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

FIGS. 1 through 28A illustrate the cross-sectional views of intermediate stages in the formation of a package in accordance with some embodiments of the present disclosure. The steps shown in FIGS. 1 through 28A are also reflected schematically in the process flow 300 shown in FIG. 33.

FIG. 1 illustrates carrier 20 and release layer 22 formed on carrier 20. Carrier 20 may be a glass carrier, a silicon wafer, an organic carrier, or the like. Carrier 20 may have a round top-view shape, and may have a size of a common silicon wafer. For example, carrier 20 may have an 8-inch diameter, a 12-inch diameter, or the like. Release layer 22 may be formed of a polymer-based material (such as a Light To Heat Conversion (LTHC) material), which may be removed along with carrier 20 from the overlying structures that will be formed in subsequent steps. In accordance with some embodiments of the present disclosure, release layer 22 is formed of an epoxy-based thermal-release material. Release layer 22 may be coated onto carrier 20. The top surface of release layer 22 is leveled and has a high degree of co-planarity.

Dielectric layer 24 is formed on release layer 22. In accordance with some embodiments of the present disclosure, dielectric layer 24 is formed of a polymer, which may also be a photo-sensitive material such as polybenzoxazole (PBO), polyimide, benzocyclobutene (BCB), or the like, that may be easily patterned using a photo lithography process.

Redistribution Lines (RDLs) 26 are formed over dielectric layer 24. The formation of RDLs 26 may include forming a seed layer (not shown) over dielectric layer 24, forming a patterned mask (not shown) such as a photo resist over the seed layer, and then performing a metal plating on the exposed seed layer. The patterned mask and the portions of the seed layer covered by the patterned mask are then removed, leaving RDLs 26 as in FIG. 1. In accordance with some embodiments of the present disclosure, the seed layer includes a titanium layer and a copper layer over the titanium layer. The seed layer may be formed using, for example, Physical Vapor Deposition (PVD). The plating may be performed using, for example, electro-less plating.

Further referring to FIG. 1, dielectric layer 28 is formed on RDLs 26. The bottom surface of dielectric layer 28 is in contact with the top surfaces of RDLs 26 and dielectric layer 24. In accordance with some embodiments of the present disclosure, dielectric layer 28 is formed of a polymer, which may be a photo-sensitive material such as PBO, polyimide, BCB, or the like. Dielectric layer 28 is then patterned to form openings 30 therein. Hence, some portions of RDLs 26 are exposed through the openings 30 in dielectric layer 28.

Next, referring to FIG. 2, RDLs 32 are formed to connect to RDLs 26. RDLs 32 include metal traces (metal lines) over dielectric layer 28. RDLs 32 also include vias extending into the openings in dielectric layer 28. RDLs 32 are also formed in a plating process, wherein each of RDLs 32 includes a seed layer (not shown) and a plated metallic material over the seed layer. The seed layer and the plated material may be formed of the same material or different materials. RDLs 32 may include a metal or a metal alloy including aluminum, copper, tungsten, and alloys thereof. The steps for forming dielectric layers 28 and 34 and RDLs 32 and 36 are represented as step 302 in the process flow 300 as shown in FIG. 33.

Referring to FIG. 3, dielectric layer 34 is formed over RDLs 32 and dielectric layer 28. Dielectric layer 34 may be formed using a polymer, which may be selected from the same candidate materials as those of dielectric layer 28. For example, dielectric layer 34 may be formed of PBO, polyimide, BCB, or the like. Alternatively, dielectric layer 34 may include a non-organic dielectric material such as silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, or the like.

FIG. 3 further illustrates the formation of RDLs 36, which are electrically connected to RDLs 32. The formation of RDLs 36 may adopt the methods and materials similar to those for forming RDLs 32. It is appreciated that although in the illustrative exemplary embodiments, two polymer layers 28 and 34 and the respective RDLs 32 and 36 formed therein are discussed, fewer or more dielectric layers may be adopted, depending on the routing requirement and the requirement of using polymers for buffering stress. For example, there may be a single polymer layer or three, four, or more polymer layers.

FIG. 4 illustrates the formation of passivation layers 38 and 42 and RDLs 40 and 44. The respective step is illustrated as step 304 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, passivation layers 38 and 42 are formed of inorganic materials such as silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, silicon oxy-carbo-nitride, Un-doped Silicate Glass (USG), or multiplayers thereof. Each of passivation layers 38 and 42 may be a single layer or a composite layer, and may be formed of a non-porous material. In accordance with some embodiments of the present disclosure, one or both of passivation layers 38 and 42 is a composite layer including a silicon oxide layer (not shown separately), and a silicon nitride layer (not shown separately) over the silicon oxide layer. Passivation layers 38 and 42 have the function of blocking moisture and detrimental chemicals from accessing the conductive features such as fine-pitch RDLs in the package, as will be discussed in subsequent paragraphs.

RDLs 40 and 44 may be formed of aluminum, copper, aluminum copper, nickel, or alloys thereof. In accordance with some embodiments of the present disclosure, some portions of RDLs 44 are formed as metal pads that are large enough for landing the subsequently formed Through-Dielectric Vias (TDVs), as shown in FIG. 11. These metal pads are accordingly referred to as metal pads 44 or aluminum pads 44 in accordance with some embodiments. Also, the number of passivation layers may be any integer number such as one, two (as illustrated), three, or more.

FIG. 5 illustrates the formation of one or a plurality of dielectric layers. For example, as illustrated, dielectric layer 46 may be formed to embed the top RDLs 44 therein. Dielectric layer 48 is formed over dielectric layer 46, and may act as an etch stop layer. In accordance with some embodiments of the present disclosure, dielectric layers 46 and 48 can also be replaced with a single dielectric layer. The available materials of dielectric layers 46 and 48 include silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, or the like.

FIGS. 6, 7, and 8 illustrate the formation of dielectric layers and fine-pitch RDLs in accordance with some embodiments of the present disclosure. The respective step is illustrated as step 306 in the process flow 300 as shown in FIG. 33. The formation methods may adopt the method for forming interconnect structure for device dies based on silicon substrates. For example, the formation methods of the interconnect structure may include single damascene and/or dual damascene processes. Accordingly, the resulting RDLs are also alternatively referred to as metal lines and vias, and the corresponding dielectric layers are alternatively referred to as Inter-Metal-Dielectric (IMD) layers.

Referring to FIG. 6, dielectric layers 50A and 54A and etch stop layer 52A are formed. Dielectric layers 50A and 54A may be formed of silicon oxide, silicon oxynitride, silicon nitride, or the like, or low-k dielectric materials having k values lower than about 3.0. The low-k dielectric materials may include Black Diamond (a registered trademark of Applied Materials), a carbon-containing low-k dielectric material, Hydrogen SilsesQuioxane (HSQ), MethylSilsesQuioxane (MSQ), or the like. Etch stop layer 52A is formed of a material having a high etching selectivity relative to dielectric layers 50A and 54A, and may be formed of silicon carbide, silicon carbo-nitride, etc. In accordance with alternative embodiments, etch stop layer 52A is not formed.

Fine-pitch RDLs 56A are formed in dielectric layers 52A and 54A for routing. It is appreciated that the single illustrated fine-pitch RDLs 56A represents a plurality of fine-pitch RDLs. Since the fine-pitch RDLs in accordance with some embodiments of the present disclosure are formed using damascene processes, it can be formed very thin with pitches (viewed from the top of the structure) smaller than, for example, 0.8 μm. This significantly improves the density of the fine-pitch RDLs and the routing ability. In accordance with some embodiments of the present disclosure, fine-pitch RDLs 56A are formed using a single damascene process, which includes etching dielectric layers 50A and 52A to form trenches, filling the trenches with a conductive material(s), and performing a planarization such as Chemical Mechanical Polish (CMP) or mechanical grinding to remove the portions the conductive material over dielectric layer 54A.

In accordance with some embodiments of the present disclosure, the conductive material for forming fine-pitch RDLs 56A is a homogenous material. In accordance with other embodiments of the present disclosure, the conductive material is a composite material including a barrier layer formed of titanium, titanium nitride, tantalum, tantalum nitride, or the like, and a copper-containing material (which may be copper or copper alloy) over the barrier layer. Fine-pitch RDLs 56A may also be formed of a dual damascene process, so that some vias may be formed underlying some fine-pitch RDLs 56A, and the vias may be used to connect the fine-pitch RDLs 56A to RDLs 44.

FIG. 7 illustrates the formation of dielectric layers 50B and 54B and etch stop layer 52B. The materials of dielectric layers 50B and 54B may be selected from the same candidate materials for forming dielectric layers 50A and 54A, and the material of etch stop layer 52B may be selected from the same candidate materials for forming etch stop layer 52A.

Fine-pitch RDLs 56B are also formed in dielectric layers 50B, 52B, and 54B. Fine-pitch RDLs 56B include metal lines formed in dielectric layers 54B and 52B and vias in dielectric layer 50B. The formation may include a dual damascene process, which include forming trenches in dielectric layers 54B and 52B and via openings in dielectric layer 50B, filling a conductive material(s), and then performing a planarization such as mechanical grinding or Chemical Mechanical Polish (CMP). Similarly, fine-pitch RDLs 56B may be formed of a homogenous material, or may be formed of a composite material including a barrier layer and a copper-containing material over the barrier layer.

FIG. 8 illustrates the formation of dielectric layers 50C and 54C, etch stop layer 52C, and fine-pitch RDLs 56C. The formation method and the materials may be similar to the underlying respective layers, and hence are not repeated herein. Also, etch stop layers 52A, 52B, and 52C may be omitted in accordance with some embodiments of the present disclosure, and the corresponding etching for forming trenches may be performed using a time-mode to control the depths of the trenches. It is appreciated that there may be more dielectric layers and layers of fine-pitch RDLs formed. In addition, even if some or all of etch stop layers 52A, 52B, and 52C may be skipped, since the dielectric layers in which the fine-pitch RDLs are located are formed in different processes, there may be distinguishable interfaces between the dielectric layers for forming fine-pitch RDLs 56A, 56B, and 56C, regardless of whether these dielectric layers are formed of the same dielectric material or different dielectric materials. In subsequent paragraphs, dielectric layers 50A, 52A, 54A, 50B, 52B, 54B, 50C, 52C, and 54C are collectively and individually referred to as dielectric layers 58 for the simplicity in identification. Fine-pitch RDLs 56A, 56B, and 56C are also collectively and individually referred to as fine-pitch RDLs 56.

Referring to FIG. 9, dielectric layers 48 and 58 are etched to form Through-Dielectric Via (TDV) openings 60. The respective step is illustrated as step 308 in the process flow 300 as shown in FIG. 33. Metal pads 44 are exposed to TDV openings 60. When viewed from the top of the structure shown in FIG. 9, via openings 60 may be aligned to ring to encircle the regions in which the fine-pitch RDLs 56 are formed. The top-view shapes of via openings 60 may be rectangles, circles, hexagons, or the like.

Next, TDV openings 60 are filled with a conductive material(s) to form TDVs 62, and the resulting structure is shown in FIG. 10. The respective step is illustrated as step 310 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, TDVs 62 are formed of a homogenous conductive material, which may be a metal or a metal alloy including copper, aluminum, tungsten, or the like. In accordance with alternative embodiments of the present disclosure, TDVs 62 have a composite structure including a conductive barrier layer formed of titanium, titanium nitride, tantalum, tantalum nitride, or the like, and a metal-containing material over the barrier layer. In accordance with some embodiments of the present disclosure, a dielectric isolation layer is formed to encircle each of TDVs 62. In accordance with alternative embodiments, no dielectric isolation layers are formed to encircle TDVs 62, and TDVs 62 are in physical contact with dielectric layers 58. The formation of TDVs 62 also include depositing the conductive material into the TDV openings 60 (FIG. 9), and performing a planarization to remove excess portions of the deposited material over dielectric layers 58.

FIG. 11 illustrates the formation of bond pads 66 and dielectric layer 64, and bond pads 66 are located in dielectric layer 64. The respective step is illustrated as step 312 in the process flow 300 as shown in FIG. 33. Bond pads 66 may be formed of a metal that is easy for forming hybrid bonding. In accordance with some embodiments of the present disclosure, bond pads 66 are formed of copper or a copper alloy. Dielectric layer 64 may be formed of silicon oxide, for example. The top surfaces of bond pads 66 and dielectric layer 64 are coplanar. The planarity may be achieved, for example, through a planarization step such as a CMP or a mechanical grinding step.

Throughout the description, the components over layer 22 are in combination referred to as interposer 100. Interposer 100, different from conventional interposers that were formed based on silicon substrates, are formed based on dielectric layers 58. No silicon substrate is in interposer 100, and hence interposer 100 is referred to as a silicon-substrate-free interposer or a Si-less interposer. TDVs 62 are formed in dielectric layers 58 to replace conventional through-silicon vias. Since silicon substrate is semiconductive, it may adversely affect the performance of the circuits and the connections formed therein and thereon. For example signal degradation may be caused by the silicon substrate, and such degradation may be avoided in the embodiments of the present disclosure since the TDVs 62 are formed in dielectric layers.

Next, first-layer device dies 68A and 68B are bonded to interposer 100, as shown in FIG. 12. The respective step is illustrated as step 314 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, device dies 68A and 68B include a logic die, which may be a Central Processing Unit (CPU) die, a Micro Control Unit (MCU) die, an input-output (IO) die, a BaseBand (BB) die, or an Application processor (AP) die. Device dies 68A and 68B may also include a memory die. Device dies 68A and 68B include semiconductor substrates 70A and 70B, respectively, which may be silicon substrates. Through-Silicon Vias (TSVs) 71A and 71B, sometimes referred to as through-semiconductor vias or through-vias, are formed to penetrate through semiconductor substrates 70A and 70B, respectively, and are used to connect the devices and metal lines formed on the front side (the illustrated bottom side) of semiconductor substrates 70A and 70B to the backside. Also, device dies 68A and 68B include interconnect structures 72A and 72B, respectively, for connecting to the active devices and passive devices in device dies 68A and 68B. Interconnect structures 72A and 72B include metal lines and vias (not shown).

Device die 68A includes bond pads 74A and dielectric layer 76A at the illustrated bottom surface of device die 68A. The illustrated bottom surfaces of bond pads 74A are coplanar with the illustrated bottom surface of dielectric layer 76A. Device die 68B includes bond pads 74B and dielectric layer 76B at the illustrated bottom surface. The illustrated bottom surfaces of bond pads 74B are coplanar with the illustrated bottom surface of dielectric layer 76B.

The bonding may be achieved through hybrid bonding. For example, bond pads 74A and 74B are bonded to bond pads 66 through metal-to-metal direct bonding. In accordance with some embodiments of the present disclosure, the metal-to-metal direct bonding is copper-to-copper direct bonding. Furthermore, dielectric layers 76A and 76B are bonded to dielectric layer 64, for example, with Si—O—Si bonds generated. The hybrid bonding may include a pre-bonding and an anneal, so that the metals in bond pads 74A (and 74B) inter-diffuse with the metals in the respective underlying bond pads 66.

Fine-pitch RDLs 56 electrically interconnect bond pads 74A and bond pads 74B, and are used for the signal communication between device dies 68A and 68B. Fine-pitch RDLs 56 have small pitches and small widths. Accordingly, the density of fine-pitch RDLs 56 is high, and hence enough communication channels may be formed for the direct communication between device dies 68A and 68B. On the other hand, TDVs 62 provide direct connection from device dies 68A and 68B to the component (which may be a package substrate, a Printed Circuit Board (PCB), or the like) that will be bonded to interposer 100. Furthermore, the bonding between bond pads 74A/74B and 66 are through bond pads rather than through solder joints, which are typically much larger than the bond pads. Accordingly, the horizontal sizes of the bonds are small, and more bonds can be implemented to provide enough communication channels.

Referring to FIG. 13, a backside grinding is performed to thin device dies 68A and 68B, for example, to a thickness between about 15 μm and about 30 μm. The respective step is illustrated as step 316 in the process flow 300 as shown in FIG. 33. Through the thinning, the aspect ratio of gaps 78 between neighboring device dies 68A and 68B is reduced in order to perform gap filling. Otherwise, the gap filling is difficult due to the otherwise high aspect ratio of openings 78. After the backside grinding, TSVs 71A and 71B may be revealed. Alternatively, TSVs 71A and 71B are not revealed at this time. Instead, TSVs 71A and 71B may be revealed in the step shown in FIG. 17.

Next, gaps 78 are filled by gap-filling material 80, as shown in FIG. 14. The respective step is illustrated as step 318 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, gap-filling material 80 includes an oxide such as silicon oxide, which may be formed of tetraethyl orthosilicate (TEOS). The formation method may include Chemical Vapor Deposition (CVD), High-Density Plasma Chemical Vapor Deposition (HDPCVD), or the like. In accordance with alternative embodiments, gap-filling material 80 is formed of a polymer such as PBO, polyimide, or the like. A planarization step is then performed to remove excess portions of gap-filling material 80, so that substrates 70A and 70B of device dies 68A and 68B are revealed. The resulting structure is shown in FIG. 15.

FIG. 16 illustrates the formation of via openings 161, which are formed by etching-through gap-filling material 80 in an anisotropic etching step. The respective step is illustrated as step 320 in the process flow 300 as shown in FIG. 33. Some bond pads 66 are exposed to via openings 161, wherein the etching may be performed using bond pads 66 as etch stop layers. Next, via openings 161 are filled with a conductive material(s) to form TDVs 162, as shown in FIG. 17. The respective step is illustrated as step 322 in the process flow 300 as shown in FIG. 33. The formation process includes filling conductive materials into via openings 161, and then performing a planarization to remove excess the conductive materials. TDVs 162 may have a structure similar to the structure of TDVs 62, and may include barrier layers and a metallic material over the barrier layers. The materials of TDVs 162 may also be selected from the similar candidate materials for forming TDVs 62.

Referring to FIG. 18, substrates 70A and 70B are recessed to form recesses 73, and the top ends of TSVs 71A and 71B protrude slightly above the top surfaces of substrates 70A and 70B, respectively. The respective step is illustrated as step 324 in the process flow 300 as shown in FIG. 33. Recesses 73 are then filled with a dielectric material such as silicon oxide to form dielectric layers 75A and 75B, and the resulting structure is shown in FIG. 19. The respective step is illustrated as step 326 in the process flow 300 as shown in FIG. 33. The formation process includes a deposition process to deposit a blanket dielectric layer, and preforming a planarization to remove portions of the blanket dielectric layer higher than the top ends of TSVs 71A and 71B.

Next, second-layer device dies 168A and 168B are bonded to device dies 68A and 68B, as shown in FIG. 20. The respective step is illustrated as step 328 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, device dies 168A and 168B include logic dies, memory dies, or combinations thereof. Device dies 168A and 168B include semiconductor substrates 170A and 170B, respectively, which may be semiconductor substrates such as silicon substrates. TSVs (not shown) may be formed in semiconductor substrates 170A and 170B if there are third-layer device dies bonded over device dies 168A and 168B. Alternatively, TSVs are not formed in semiconductor substrates 170A and 170B. Also, device dies 168A and 168B include interconnect structures 172A and 172B, respectively, for connecting to the active devices and passive devices in device dies 168A and 168B. Interconnect structures 172A and 172B include metal lines and vias (not shown).

Device die 168A includes bond pads 174A and dielectric layer 176A at the illustrated bottom surface of device die 168A. The illustrated bottom surfaces of bond pads 174A are coplanar with the illustrated bottom surface of dielectric layer 176A. Device die 168B includes bond pads 174B and dielectric layer 176B at the illustrated bottom surface. The illustrated bottom surfaces of bond pads 174B are coplanar with the illustrated bottom surface of dielectric layer 176B.

The bonding may be achieved through hybrid bonding. For example, bond pads 174A and 174B are directly bonded to TSVs 71A and 71B and TDVs 162 through metal-to-metal direct bonding. In accordance with some embodiments of the present disclosure, the metal-to-metal direct bonding is copper-to-copper direct bonding. Furthermore, dielectric layers 176A and 176B are bonded to dielectric layers 75A and 75B, for example, with Si—O—Si bonds generated. Depending on the material of gap-filling material 80, dielectric layers 176A and 176B may be bonded to gap-filling material 80, or may be in contact with, but not bonded to (no bonds are formed) gap-filling material 80.

Next, device dies 168A and 168B may be thinned, similar to the thinning of device dies 68A and 68B. The gaps between neighboring device dies 168A and 168B are then filled by gap-filling material 180, as shown in FIG. 21. The respective step is illustrated as step 330 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, gap-filling material 180 is formed using a method selected from the same candidate methods for forming gap-filling material 80. Gap-filling material 180 may also be selected from the same candidate materials for forming gap-filling material 80, and may include an oxide such as silicon oxide, PBO, polyimide, or the like. A planarization step is then performed to remove excess portions of gap-filling material 180, so that substrates 170A and 170B of device dies 168A and 168B are revealed.

Dielectric layer 182 is then deposited as a blanket layer, for example, using CVD, PECVD, ALD, or the like. The resulting structure is also shown in FIG. 21. The respective step is illustrated as step 332 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, dielectric layer 182 is formed of an oxide such as silicon oxide, silicon oxynitride, or the like.

Next, referring to FIG. 22, trenches 184 are formed by etching dielectric layer 182 and substrates 170A and 170B, so that trenches 184 extend into dielectric layer 182 and substrates 170A and 170B. Depth D1 of the portions of trenches 184 inside substrates 170A and 170B may be greater than about 1 μm, and may be between about 2 μm and about 5 μm, depending on the thickness T1 of substrates 170A and 170B. For example, depth D1 may be between about 20 percent and about 60 percent of thickness T1. It is appreciated that the values recited throughout the description are examples, and may be changed to different values.

Trenches 184 may be distributed in various patterns. For example, trenches 184 may be formed as discrete openings, which may be allocated to have a pattern of an array, a pattern of beehive, or other repeat patterns. The top-view shapes of trenches 184 may be rectangles, circles, hexagons, or the like. In accordance with alternative embodiments, trenches 184, when viewed in the top view of the structure shown in FIG. 16, may be parallel trenches that have lengthwise directions in a single direction. Trenches 84 may also be interconnected to form a grid. The grid may include a first plurality of trenches parallel to each other and evenly or unevenly spaced, and a second plurality of trenches parallel to each other and evenly or unevenly spaced. The first plurality of trenches and the second plurality of trenches intercept with each other to form the grid, and the first plurality of trenches and the second plurality of trenches may or may not be perpendicular to each other in the top view.

Trenches 184 are then filled to form bond pads 187, as shown in FIG. 23. The respective step is also illustrated as step 332 in the process flow 300 as shown in FIG. 33. It is appreciated that although features 187 are referred to as bond pads, features 187 may be discrete pads, interconnected metal lines, or a metal grid. In accordance with some embodiments of the present disclosure, bond pads 187 are formed of copper or other metals suitable for hybrid bonding (due to relatively easiness in diffusing). After the filling, a planarization is performed to planarize the top surfaces of bond pads 187 with the top surface of dielectric layer 182. The planarization may include a CMP or a mechanical grinding.

Next, as shown in FIG. 24, blank die 88 is bonded to device dies 168A and 168B. The respective step is illustrated as step 334 in the process flow 300 as shown in FIG. 33. Blank die 88 includes bulk substrate 194, which may be a silicon substrate or a metal substrate. When formed of metal, substrate 194 may be formed of copper, aluminum, stainless steel, or the like. When substrate 194 is formed of silicon, there is no active device and passive device formed in blank die 88. Blank die 88 includes two functions. First, blank die 88 provides mechanical support to the underlying structure since device dies 68A, 68B, 168A, and 168B have been thinned in order to allow for better gap filling. Also, silicon or metal (of substrate 194) has a high thermal conductivity, and hence blank die 88 may act as a heat spreader. Since the formation of the structure in FIG. 24 is at wafer-level, a plurality of blank dies identical to the illustrated blank dies 88 are also bonded to the respective underlying device dies that are identical to device dies 168A and 168B.

In accordance with alternative embodiments, instead of bonding blank die 88, third-layer device dies are placed in the position of blank die 88, and are bonded to device dies 168A and 168B.

Dielectric layer 190 is formed at the surface of substrate 194. Dielectric layer 190 may be formed of silicon oxide or silicon oxynitride, for example. Also, bond pads 192 are formed in dielectric layer 190, and the illustrated bottom surfaces of bond pads 192 are coplanar with the illustrated bottom surface of dielectric layer 190. The pattern and the horizontal sizes of bond pads 192 may be the same as or similar to that of the respective bond pads 187, so that bond pads 192 and bond pads 187 may be bonded to each other with a one-to-one correspondence.

The bonding of blank die 88 onto device dies 168A and 168B may be achieved through hybrid bonding. For example, dielectric layers 182 and 190 are bonded to each other, and may form Si—O—Si bonds. Bond pads 192 are bonded to the respective bond pads 187 through metal-to-metal direct bonding.

Advantageously, bond pads 187, by contacting (and even being inserted into) substrates 170A and 170B, provide a good thermal dissipating path, so that the heat generated in device dies 68A, 68B, 168A and 168B can easily dissipate into bulk substrate 194, and hence bulk substrate 194 is used as a heat spreader.

Referring to FIG. 25, photo resist 183 is applied and patterned. Dielectric layer 182 and gap-filing material 180 are then etched using the patterned photo resist 183 as an etching mask to reveal some portions of interposer 100. The respective step is illustrated as step 336 in the process flow 300 as shown in FIG. 33. In accordance with some embodiments of the present disclosure, some device dies such as device die 168B are revealed. Some of TSVs 71B and TDVs 162 may also be exposed.

FIG. 26 illustrates the bonding of die stack 212 onto the second-layer structure. The respective step is illustrated as step 338 in the process flow 300 as shown in FIG. 33. Die stack 212 may be bonded to TDVs 162, device dies (such as die 168B), or both TDVs 162 and the device dies. Die stack 212 may be a memory stack including a plurality of stacked dies 214, wherein TSVs (not shown) may be formed in dies 214 to perform interconnection. Die stack 212 may also be a High Bandwidth Memory (HBM) cube. In accordance with some embodiments of the present disclosure, die stack 212 is bonded to the underlying structure through hybrid bonding, wherein electrical connectors 216 (bond pads in some embodiments) in die stack 212 are bonded to TDVs 162 and TSVs 71B through metal-to-metal direct bonding, and dielectric layer 218 of die stack 212 is bonded to gap-filling material 80 (an oxide, for example) and dielectric layer 75B through oxide-to-oxide bonding (or fusion bonding). In accordance with alternative embodiments, electrical connectors 216 are solder regions, and the bonding is solder bonding. In accordance with yet alternative embodiments, electrical connectors 216 are micro-bumps protruding beyond the surface dielectric layer 218 of die stack 212, and no oxide-to-oxide bonding occurs between die stack 212 and gap filling material 80 and dielectric layer 75B. Micro-bumps 216 may be bonded to TDVs 162 and TSVs 71B through metal-to-metal direct bonding or solder bonding.

Next, gap-filling material 220 (FIG. 27) is filled into the gaps between blank die 88 and die stack 212. Gap-filling material 220 may be formed of an oxide such as silicon oxide or a polymer. The structure formed on carrier 20 is then de-bonded from carrier 20 (FIG. 26), for example, by projecting light such as UV light or laser on release layer 22 to decompose release layer 22. The resulting structure is shown in FIG. 27. Carrier 20 and release layer 22 are removed from the overlying structure, which is referred to as composite wafer 102 (FIG. 27). The respective step is illustrated as step 340 in the process flow 300 as shown in FIG. 33. If needed, a carrier swap may be performed to attach another carrier (not shown) over the illustrated structure before carrier 20 is detached, and the new carrier is used to provide mechanical support during the formation of electrical connectors in the subsequent step.

FIG. 28A illustrates the formation of electrical connectors 110, which may penetrate through dielectric layer 24, and connect to RDLs 26. Electrical connectors 110 may be metal bumps, solder bumps, metal pillars, wire bonds, or other applicable connectors. A die-saw step is performed on composite wafer 102 to separate composite wafer 102 into a plurality of packages 104. Packages 104 are identical to each other, and each of packages 104 may include two layers of device dies and die stack 212. The respective step is also illustrated as step 340 in the process flow 300 as shown in FIG. 33.

FIG. 28B illustrates the package 104 formed in accordance with some embodiments of the present disclosure. These embodiments are similar to the embodiments shown in FIG. 28A, except that bond pads 187 penetrate through dielectric layer 182 and does not extend into substrates 170A and 170B. Bond pads 187 are in contact with substrates 170A and 170B in accordance with some embodiments. In accordance with alternative embodiments, one or both of bond pads 187 and 192, instead of penetrating through the respective dielectric layers 182 and 190, extend partially into the respective dielectric layers 182 and 190 from the interface wherein bonding occurs. Bond pads 187 and 192 and bulk substrate 194 may be electrically grounded in accordance with some embodiments of the present disclosure to provide electrical grounding for substrates 170A and 170B

FIG. 28C illustrates the package formed in accordance with some embodiments of the present disclosure. These embodiments are similar to the embodiments shown in FIGS. 28A and 28B, except that bond pads 187 and 192 and dielectric layer 190 (as in FIGS. 28A and 28B) are not formed. Bulk substrate 194, which is also blank die 88, is bonded to dielectric layer 82 through fusion bonding.

In accordance with alternative embodiments of the present disclosure, blank die 88 is a metal die. Accordingly, layer 182 in FIG. 28C may be formed of a Thermal Interface Material (TIM), which is an adhesive having a high thermal conductivity.

FIGS. 29 and 30 illustrate the cross-sectional views of intermediate stages in the formation of a package in accordance with some embodiments of the present disclosure. Unless specified otherwise, the materials and the formation methods of the components in these embodiments are essentially the same as the like components, which are denoted by like reference numerals in the embodiments shown in FIGS. 1 through 28A. The details regarding the formation process and the materials of the components shown in FIGS. 29 and 30 may thus be found in the discussion of the embodiment shown in FIGS. 1 through 28A. FIG. 29 illustrates a cross-sectional view of composite wafer 102, which is essentially the same as what is shown in FIG. 28A, except metal pads 45 are formed on dielectric layer 24, while the features including dielectric layers 28, 34, 38, and 42 and RDLs 32, 36, 40 and 44 as shown in FIG. 28A are not formed on carrier 20. Rather, as shown in FIG. 30, which illustrates a structure formed subsequent to the step shown in FIG. 29, the dielectric layers 28, 34, 38, and 42 and RDLs 32, 36, 40 and 44 are formed after carrier 20 (FIG. 21) is detached. The sequence for forming dielectric layers 28, 34, 38, and 42 in accordance with these embodiments are reversed relative to the sequence shown in FIGS. 1 through 11. It is noted that due to different formation sequences, the orientations of RDLs 32, 36, 40 and 44 are inverted (in vertical direction) compared to what is shown in FIG. 28A. Packages 104 are then formed through the die-saw of composite wafer 102.

FIG. 31 illustrates a package 112 in which package 104 (FIGS. 28A, 28B. 28C, and 30) is embedded. The package includes memory cubes 114, which includes a plurality of stacked memory dies (not shown separately). Package 104 and memory cubes 114 are encapsulated in encapsulating material 118, which may be a molding compound. Dielectric layers and RDLs (collectively illustrated as 116) are underlying and connected to package 104 and memory cubes 114. In accordance with some embodiments of the present disclosure, dielectric layers and RDLs 116 are formed using similar materials and have similar structures as that are shown in FIGS. 1 through 11.

FIG. 32 illustrates Package-on-Package (PoP) structure 132, which has Integrated Fan-Out (InFO) package 138 bonded with top package 140. InFO package 138 also includes package 104 embedded therein. Package 104 and through-vias 134 are encapsulated in encapsulating material 130, which may be a molding compound. Package 104 is bonded to dielectric layers and RDLs, which are collectively referred to as 146. Dielectric layers and RDLs 146 may also be formed using similar materials and have similar structures as what are shown in FIGS. 1 through 11.

The embodiments of the present disclosure have some advantageous features. By forming the fine-pitch RDLs in interposers using the processes typically used on silicon wafers (such as damascene processes), the fine-pitch RDLs may be formed to be thin enough to provide the capability for the communication of two or more device dies all through the fine-pitch RDLs. The package also provides a solution for integrating memory cubes. No silicon substrate is used in the interposer, and hence the degradation in electrical performance resulted from the silicon substrate is avoided. There are also some heat-dissipating mechanisms built in the package for better heat dissipation.

In an embodiment, a method includes forming a plurality of dielectric layers, forming a plurality of redistribution lines in the plurality of dielectric layers, etching the plurality of dielectric layers to form an opening, filling the opening to form a through-dielectric via penetrating through the plurality of dielectric layers, forming a dielectric layer over the through-dielectric via and the plurality of dielectric layers, forming a plurality of bond pads in the dielectric layer, bonding a first device die to the dielectric layer and a first portion of the plurality of bond pads through hybrid bonding, and bonding a die stack to through-silicon vias in the first device die. In an embodiment, the method further includes bonding a second device die to the dielectric layer and a second portion of the plurality of bond pads through hybrid bonding, wherein the plurality of redistribution lines connects the first device die to the second device die. In an embodiment, the forming the plurality of redistribution lines comprises damascene processes. In an embodiment, the through-dielectric via does not extend into any semiconductor substrate. In an embodiment, the method further includes bonding an additional device die to the first device die, wherein the additional device die is bonded directly to through-silicon vias in the first device die, forming an oxide layer over and contacting a semiconductor substrate of the additional device die, forming a bond pad extending into the oxide layer, and bonding a blank die to the oxide layer and the bond pad through hybrid bonding. In an embodiment, the bond pad extends into the semiconductor substrate of the additional device die. In an embodiment, the bond pad contacts, without extending into, the semiconductor substrate of the additional device die.

In an embodiment, a method includes forming a plurality of dielectric layers, forming a plurality of redistribution lines in each of the plurality of dielectric layers, forming a first through-dielectric via and a second through-dielectric via penetrating through the plurality of dielectric layers, forming a dielectric layer over the plurality of dielectric layers, forming a plurality of bond pads in the dielectric layer and electrically coupling to the first through-dielectric via, the second through-dielectric via, and the plurality of redistribution lines, bonding a first device die and a second device die to the dielectric layer and the plurality of bond pads through hybrid bonding, wherein the first device die and the second device die are electrically interconnected through the plurality of redistribution lines, and bonding a die stack to the second device die. In an embodiment, the plurality of redistribution lines is formed using damascene processes. In an embodiment, the method further includes filling a gap-filling material on opposite sides the first device die and the second device die, forming a third through-dielectric via penetrating through the gap-filling material, and bonding a third device die directly to, and in physical contact with, the third through-dielectric via. In an embodiment, the method further includes forming a fourth through-dielectric via penetrating through the gap-filling material, wherein the second device die is bonded directly to, and in physical contact with, the third through-dielectric via, and the die stack is bonded directly to, and in physical contact with, the fourth through-dielectric via. In an embodiment, the forming the first through-dielectric via and the second through-dielectric via comprises: etching the plurality of dielectric layers to form a first opening and a second opening, and filling the first opening and the second opening with a conductive material. In an embodiment, the method further includes thinning the first device die and the second device die to expose through-silicon vias in the first device die and the second device die, and bonding a third device die to the through-silicon vias. In an embodiment, the method further includes forming a dielectric layer over the third device die, and bonding a bulk wafer to the dielectric layer.

In an embodiment, a package includes a plurality of dielectric layers, a plurality of redistribution lines in each of the plurality of dielectric layers, a first through-dielectric via penetrating through the plurality of dielectric layers, a plurality of bond pads over and connected to the first through-dielectric via and the plurality of redistribution lines, a first dielectric layer, with the plurality of bond pads located in the first dielectric layer, a first device die bonded to the first dielectric layer and a first portion of the plurality of bond pads through hybrid bonding, a gap-filling material on opposite sides of the first device die, a second through-dielectric via penetrating through the gap-filling material, and a die stack bonded to the second through-dielectric via. In an embodiment, the package further includes a second device die bonded to the first dielectric layer and a second portion of the plurality of bond pads through hybrid bonding, wherein the first device die and the second device die are electrically coupled to each other through the plurality of redistribution lines. In an embodiment, the package further includes a second device die over and bonded to the first device die, a bond pad contacting a semiconductor substrate of the second device die, wherein at least a portion of the bond pad is over the semiconductor substrate of the second device die, a second dielectric layer, with the bond pad having at least a portion in the second dielectric layer, and a bulk substrate over and bonded to the second dielectric layer and the bond pad. In an embodiment, the bulk substrate is formed of silicon, and no active device and passive device is formed on the bulk substrate. In an embodiment, the bond pad further extends into the semiconductor substrate of the second device die. In an embodiment, the bond pad forms a grid.

In an embodiment, a method includes forming a plurality of dielectric layers over a carrier, after the plurality of dielectric layers is formed, etching the plurality of dielectric layers to form a first opening and a second opening penetrating through the plurality of dielectric layers, filling the first opening and the second opening to form a first and a second through-dielectric via, bonding a device die over and electrically coupling to the first through-dielectric via, wherein the bonding the device die comprises hybrid bonding, and bonding a die stack over and electrically coupling to the second through-dielectric via. In an embodiment, the method further includes forming a dielectric layer over the plurality of dielectric layers, and forming a bond pad in the dielectric layer, wherein the bond pad is in contact with the first through-dielectric via, and the device die is physically bonded to the bond pad and the dielectric layer. In an embodiment, the plurality of dielectric layers comprises silicon oxide.

In an embodiment, a package includes a plurality of dielectric layers, a through-dielectric via penetrating through the plurality of dielectric layers, wherein the through-dielectric via has an edge continuously penetrating through the plurality of dielectric layers, a device die over the plurality of dielectric layers, wherein the device die is bonded to underlying structures through hybrid bonding, and the device die is electrically coupled to the through-dielectric via, and a die stack over and bonded to the device die. In an embodiment, the package further includes a dielectric layer over the plurality of dielectric layers, and a bond pad in the dielectric layer, wherein the bond pad is in contact with the through-dielectric via, and the device die is physically bonded to the bond pad and the dielectric layer. In an embodiment, the die stack is bonded to a through-silicon via in the device die. In an embodiment, the die stack is bonded to the device die through hybrid bonding.

In an embodiment, a package includes a plurality of dielectric layers, a through-dielectric via penetrating through the plurality of dielectric layers, a first device die over and electrically coupling to the through-dielectric via, wherein the first device die comprises a semiconductor substrate, a dielectric layer over the first device die, a bond pad in the dielectric layer, wherein the bond pad penetrate through the dielectric layer and further extends into the semiconductor substrate of the first device die, and a die stack over and bonded to the first device die. In an embodiment, the die stack is bonded to the bond pad and the dielectric layer through hybrid bonding. In an embodiment, the package further includes a second device die between the first device die and the through-dielectric via.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A package comprising: an interconnect structure comprising: a plurality of dielectric layers; an electrical path in the interconnect structure, wherein the electrical path comprises: a plurality of damascene structures, each extending into a first dielectric layer in the plurality of dielectric layers, and the plurality of damascene structures are interconnected, wherein each of the plurality of damascene structure comprises a via, and a metal line over and continuously joined to the via, wherein a first top surface of the first dielectric layer is coplanar with a second top surface of the metal line; a device die over and electrically coupling to the plurality of damascene structures, wherein the device die comprises a semiconductor substrate; and a metallic feature extending from a back surface of the semiconductor substrate down into the semiconductor substrate, wherein a bottom surface of the metallic feature stops at an intermediate level between the back surface and a front surface of the semiconductor substrate.
 2. The package of claim 1, wherein the via has a top width and a bottom width, and the top width is greater than the bottom width.
 3. The package of claim 1, wherein the via and the metal line form an integrated structure with no distinguishable interface where the via joins the metal line.
 4. The package of claim 1 further comprising a solder region underlying and electrically coupling to the device die, and wherein no transistor is located between the device die and the solder region.
 5. The package of claim 1, wherein the via in each of the plurality of damascene structure comprises a lower portion, and an upper portion wider than the lower portion.
 6. The package of claim 1 further comprising: a solder region underlying and electrically coupling to the device die; a second dielectric layer between the solder region and the plurality of dielectric layers; and a redistribution line comprising: a trace portion over and contacting the second dielectric layer; and a via portion extending into the second dielectric layer.
 7. The package of claim 6, wherein the plurality of dielectric layers are low-k inorganic dielectric layers, and the second dielectric layer comprises a polymer.
 8. The package of claim 1 further comprising a blank silicon substrate over and contacting the metallic feature.
 9. A package comprising: a solder region; a plurality of polymer layers, wherein the solder region extends into a bottom layer in the plurality of polymer layers; a plurality of redistribution lines in the plurality of polymer layers, wherein the solder region contacts one of the plurality of redistribution lines; a plurality of dielectric layers, wherein an additional bottom layer in the plurality of dielectric layers is over and physically contacting a top layer in the plurality of polymer layers, and the plurality of dielectric layers comprise low-k dielectric materials; a plurality of dual damascene structures in the plurality of dielectric layers, wherein each of the plurality of dual damascene structures comprises a metal line and a via continuously connected to each other, and wherein top surfaces of the dual damascene structures are coplanar with top surfaces of respective ones of the plurality of dielectric layers; and a first device die over and electrically coupling to the plurality of dual damascene structures.
 10. The package of claim 9, wherein lower portions of the via are narrower than respective upper portions of the via.
 11. The package of claim 9, wherein no transistor is formed higher than the solder region and lower than the first device die.
 12. The package of claim 9, wherein the plurality of dielectric layers further comprise an additional top layer, and wherein the plurality of dual damascene structures are interconnected to form an electrical path extending from a bottom surface of the additional bottom layer to a top surface of the additional top layer.
 13. The package of claim 9 further comprising a second device die over the plurality of dielectric layers, wherein the plurality of dual damascene structures electrically connect the first device die to the second device die.
 14. The package of claim 9, wherein the first device die comprises a semiconductor substrate, and the package further comprises a metallic feature extending from a back surface of the semiconductor substrate down into the semiconductor substrate, wherein a bottom surface of the metallic feature stops at an intermediate level between the back surface and a front surface of the semiconductor substrate.
 15. The package of claim 14 further comprising a blank silicon substrate over and contacting the metallic feature.
 16. A package comprising: a first conductive line; a first via and a second via over and contacting a top surface of the first conductive line; a second conductive line and a third conductive line over and joined to the first via and the second via, respectively, wherein the first via and the second conductive line form a dual damascene structure; a first device die and a second device die higher than the second conductive line, wherein the first device die is electrically connected to the second device die through an electrical path comprising the second conductive line, the first via, the third conductive line, the second via, and the first conductive line; a solder region underlying the first conductive line, wherein the solder region is electrically coupled to the first device die, and no transistor is formed higher than the solder region and lower than the first device die; a plurality of low-k inorganic dielectric layers, with the first conductive line, the first via, and the second conductive line being in the plurality of low-k inorganic dielectric layers; and a plurality of polymer layers underlying the plurality of low-k inorganic dielectric layers and over the solder region.
 17. The package of claim 16 further comprising a plurality of redistribution lines in the plurality of polymer layers.
 18. The package of claim 16 further comprising a through-dielectric via extending from a top-surface-level of the second conductive line to a bottom-surface-level of the first conductive line, wherein the through-dielectric via comprises a first portion at a same level as the first conductive line, and a second portion at a same level as the second conductive line, wherein the first portion is continuously joined to the second portion without distinguishable interface in between.
 19. The package of claim 18, wherein the through-dielectric via comprises a straight edge extending from the top-surface-level to the bottom-surface-level.
 20. The package of claim 16, wherein the first device die comprises a through-silicon via therein, and the package further comprises a third device die over the first device die, wherein the third device die comprises a bond pad directly bonded to the through-silicon via. 